1. Field of the Invention
The present invention relates to controlling of a hybrid vehicle that has both an engine and a motor as power sources.
2. Description of the Related Art
In hybrid vehicles that comprises both an engine and a motor as power sources, both of which transmit torque to the drive wheels, a controlling operation, for changing a proportion of driving power to be generated by the engine and a proportion of driving power to be generated by the motor in accordance with an operation state such as a heat generation state of the motor, electrical power that can be output by a battery, or vehicle speed, is carried out. Such a device is disclosed in Japanese Unexamined Patent Application Publication No. 2004-48866.
In the hybrid vehicle, the engine and the motor can be operated at efficient operating points, so that, compared to related engine only vehicles, it is fuel-efficient and provides high exhaust performance.
When the engine proportion of torque that is transmitted to a driving shaft is small, that is, when a motor assist amount ratio is large, the influence of a surge torque or output variation (which is generated due to a deterioration in an engine combustion state) on the behavior of the vehicle is reduced. In other words, in this state, even if the exhaust performance is given priority and, for example, a lean air-fuel ratio and retarding of an ignition time for increasing the surge torque are achieved, the behavior of the vehicle is seldom adversely affected.
However, in the related art, even if the influence of the deterioration of the behavior of the vehicle is small, a controlling operation for improving the exhaust performance in accordance with the influence on the behavior of the vehicle has not been carried out.